Pumping apparatus



Oct. 22, 1968 5. 'EYLER ETAL 3,406,581

PUMPING APPARATUS Original Filed 00t- 19, 1964 5 Sheets-Sheet 1 Fig. 1

INVENTORS WILLIAM G. EASLEY JAMES 0. BLACK and GEORGE EYLER Oct. 22,1968 G. EYLER ETAL 3,406,581

PUMPING APPARATUS Original Filed Oct. 19, 1964 5 Sheets-Sheet 2 (\1 p3LL INVENTORS WILLIAM G. EASLEY JAMES 0. BLACK and GEORGE EYLER- Oct. 22,1968 EYLER E 3,406,581

/ PUMPING APPARATUS Original Filed Oct. 19, 1964 5 Sheets-Sheet 5 Fig. 3

INVENTORS WILLIAM G. EASLEY JAMES 0. BLACK 0nd GEORGE EYLER Oct. 22,1968 s. EYLER ETAL 3,406,531

PUMPING APPARATUS Original Filed Oct. 19, 1964 5 Sheets-Sheet 4 LLINVENTORS' WILLIAM G. EASLEY JAMES 0. BLACK and GEORGE EYLER Oct. 22,1968 e. EYLER ETAL 3,406,581

PUMP ING APPARATUS Original Filed Oct. 19, 1964 5 Sheets-Sheet 5INVENTORS WILLIAM G. EASLEY JAMES D. BLACK and GEORGE EYLER UnitedStates Patent 3,406,581 PUMPING APPARATUS George Eyler and William G.Easley, Pampa, and James D. Black, Miami, Tex., assiguors to CabotCorporation, Boston, Mass., a corporation of Delaware Continuation ofapplication Ser. No. 404,707, Oct. 19, 1964. This application Apr. 10,1967, Ser. No. 629,833

6 Claims. (Cl. 74-41) ABSTRACT OF THE DISCLOSURE An improved wellpumping unit is provided of th walking beam type in which the rotarydrive means is located for maximum ease of servicing, optimum eificiencyof power delivery and most consistent overall operating smoothness whilethe rotary counterbalancmg weights are simultaneously mounted inspecific geometrical relationship with respect to the exact timing ofthe well pumping stroke so as to exert maximum efiect at the timeof'greatest need. The end result is a pumping unit constructed so that,without undue extension of the pitman arm length, the crank shaft isplaced back completely out from under the normal area under the tailbearing connection on the walking beam while Sll'Illlltaneouslyminimizing peak torque factors and the mass of rotary counterweightsneeded.

This application is a continuation of application Ser. No. 404,707,which was filed 'on Oct. 19, 1964, now abandoned.

This invention relates to improved pumping apparatus of the walking beamtype such as is used primarily for lifting fluids, particularly oil,from substantial depths to the earths surface. More particularly, theinvention is concerned with an improved arrangement of 'the drivelinkage elements in a pumping unit of the most familiar walking beamtype in which the samson post supports the walking beam near its medialportion by means of a saddle bearing pivot connection and the driveequipment by means of which power is applied to the walking beam islocated on the opposite side of the samson post from the well workingend ofthe Walking beam.

U.S. Patent 3,029,650 indicates that, in order to minimize undesirableback-drive (or imposition of negative torque on the drive elements of apumping unit) during various periods of each complete stroke .cycle andto insure good over-all power efiiciency, it is necessary to locate thedrive equipment on the well side of the samson post. Such an arrangementof components, however, is not only strange and unfamiliar to most oilfield operators, but it also renders more hazardous the job of servicingthe well head area and associated equipment elements due to the closerproximity of the drive equipment.

Accordingly, it is now a primary object of the present invention tominimize the possibility of encountering high peaks or sudden changes toexcessive levels in the net torque and to tend to equalize the nettorque level applied to the crank shaft during various portions of thepumping cycle of a unit in which the walking beam is mounted in moreconventional fashion, i.e., on a pivot point near the medial portionthereof. Moreover, in achieving this more nearly uniform net torquelevel throughout the pumping cycle of a more conventional unit it is afurther object of the present invention to reduce the degree ofdependence on crank weight counterbalancing and, therefore, the amountof such counterweights required for a given job, by providing anarrangement of component parts which inherently also more nearlyequalizes the actual well load torques applied to the crank duringvarious parts of the pumping cycle.

Patented Oct. 22, 1968 Essentially, this means a unit design whichinherently compensates to an unexpected degree for the extra well loadalways carried on the upstroke of a functioning pumping unit due to theweight of fluid lifted and deliveredto ground level on each stroke.

Some of the immediate practical advantages of achieving the aboveobjects, in addition to the saving on counterbalance requirements, wouldbe the realization of a reduction in the size of prime mover, speedreducer and other elements of drive equipment for a given unit'ofspecified capacity and an over-all saving in power demand on a givenjob. Other objects and advantages will be obvious or will becomeapparent from the detailed description of the invention which follows.

In accordance with the present invention it has now been found that theabove objects and advantages can, in fact, be realized in a mid-mountedtype of walking beam pumping unit provided the rotary crank which, via apitman arm or arms, supplies the oscillating motion to the walking beamis located at a substantially more rearward position (from the samsonpost and the well) than has been previously used or recommended. Morespecifically, the crank shaft should be located sufiiciently toward therear so that substantially the entire circle described by the crankwrist pin lies to the opposite side from the well of a straight linepassing through the tail bearing pivot point at its lowest position oftravel and running at right angles to the straight line drawn betweenthe saddle bearing pivot point of the beam and said tail bearing pivotpoint at the midstroke position of the unit.

A further most surprising discovery of this invention is the fact that,when the aforesaid condition is met, then, for those pitman arm to crankarm ratios of greatest practical interest (namely from about 2.5 to l to6 to 1), the maximum effective lever arm (i.e., the maximum torquefactor) of the unit during the upstroke plus the maximum effective leverarm or torque factor during the downstroke add up to a sum less than theactual total stroke of the unit. This is an indication of the amazinglygood overall efiiciency of which the pumping units of the present arecapable since it has long been known that, in conventional pumping unitshaving an essentially symmetrical location of the crank with respect tothe tail bearing (i.e., such that said line through the tail bearingpivot point and at right angles to the straight line connecting saddlebearing and tail bearing joints at the midstroke passes through or nearthe crank shaft), then the sum of the maximum efiective lever arms ofthe unit on the upstroke and downstroke must necessarily be greater thanthe actual stroke realized by the unit except in the impractical oridealized case where the ratio of the pitman length to crank armapproaches infinity. See US. Patent 3,109,313 which discusses theseprevious limitations on efiiciency and describes the possibility ofapproaching such idealized efiiciencies in a practical unit by substituting for the conventional tail bearing connections between rigid pitmanarm(s) and the beam, a flexible spring connection to an arcuate muleheadon the driven end of the walking beam, thus permitting the angle betweenthe pitman arm and the acting line of the beam to approximate at alltimes during the complete stroke cycle. The preferred embodiments of thepresent invention are represented by those crank shaft locations which,as stated above, are sufficiently toward the rear so that substantiallythe entire circle of rotation of the crank arm lies to the rear of saidstraight line passing through said tail hearing as described above butnot so far to the rear as to necessitate pitman arms of impracticallength or tail bearings of impractical size. As will be seen from morequantitative considerations presented hereinafter, this generally meansthat the horizontal distance of the crank I 3 behind said line throughsaid tail bearing should not be over about two-thirds of the pitman armlength.

In order to explain our invention in greater detail includingquantitative aspects and preferred specific embodiments thereof,reference is now made to the accompanying drawings, in which:

FIGURE 1 is a side elevation of a pumping unit constructed in accordancewith the present invention;

FIGURES 2, 3 and 4 are largely diagrammatic representations of unitlayouts similar to that of FIGURE 1 and illustrating representativevariations in the range of preferred positions for the drive crank;

FIGURE 5 is a side elevation view of a pumping unit similar to that ofFIGURE 1 but showing a slightly different method of applying crankcounterbalance to units of the present invention.

Referring now to the drawings and particularly to FIGURE 1, it .will beseen that the basic components of the pumping units of this inventionare decidedly conventional, including a base frame 10, a samson post orupright frame 12 and a walking beam 14 mounted for oscillation in avertical plane by means of saddle bearing 16 at the top of the samsonpost. At the forward or righthand end of the walking beam there is amulehead 18 from the top of which there is suspended a wire line 20 to ahanger 22 by means of which the rod string (not shown) is held in orderto pump the well 24. Oscillation of the walking beam 14 is effected bymeans of pitman arm 26 pivotally connected by means of tail bearing 28to the rear or left hand end of the beam and by means of wrist pin 25 tothe crank 23 of speed reducer 21. Re ducer 21, in turn, is driven bymeans of a prime mover (not shown) of any suitable type. Counterbalancecan be provided in any of the usual manners, such as by mounting crankcounterweights 27 oif of crank shaft 29 or by placing weights 31directly on the Walking beam 14 or by a combination of crank weights 27with beam weights 31.

Referring now to FIGURES 2, 3 and 4, simplified diagrammatic layouts ofunits similar to that of FIGURE 1 are presented. In order to demonstratethe quantitative aspects of the present invention, these layouts of FIG-URES 2, 3 and 4 incorporate a considerable variation in the location ofthe crank shaft within the scope of the present invention. Thus, FIGURE2 represents a most preferred arrangement embodying the presentinvention in that the pitman arm to crank arm ratio of 4.0 is not onlywithin the optimum central area of the practical range but the crankshaft location is also in the middle ground of the invention, wellremoved from any of the boundary limits. FIGURE 3 actually depicts twodifferent layouts representing approximately the extreme or limitingpositions within the scope of this invention for locating the crankshaft of a unit having exactly the same pitman and crank arm lengths asthe unit represented by FIGURE 2. FIGURE 4, on the other hand, depicts atypical but nonlimiting location for a unit with a substantiallydifferent pitman arm to crank arm ratio. In said FIGURES 2 through 4,point S represents the saddle bearing pivot point on top of the samsonpost 12. Points H, M and L represent the pivot point of the tail hearingat its highest, middle and lowest positions respectively during a strokecycle. Thus, straight lines LS, HS and MS represent the effective linesof action of the walking beam at the top, bottom and midstrokepositions, respectively, of the mulehead, while 18 and 18 represent themulehead in its extreme positions. Likewise, points C, C and C representcenters of the crank shaft, and points W, and W represent the positionsof the wrist pin connecting crank and pitman arms when the tail bearingpivot point is located at extreme points H and L, respectively. Thus,the circle on which points W and W lie represents the circle of rotationdescribed by said wrist pin. For the purposes of the present invention,it is convenient to define the location of the crank shaft in 7 terms ofits distance behind the dotted lines 7 drawn through point L in FIGURES2 through 4, which represent in each case a straight line drawn at rightangles to a straight line (such as line MS), connecting the pivot pointsof the saddle bearing and the tail bearing at the midstroke position ofthe unit. The key quantitative relationships of the unit arrangementsrepresented by the layouts of FIGURES 2, land 4 are set forth in thefollowing table.

' TABLE I I t Relative distance Case P/R ratio. of crankshaft behindline LZ Figure 2 4. 0 .43? Figure 3 (forward) 4. 0 .25P Figure 3 (rear)4. 0 .66? Figure 4 5. 3 ".491?

Standard methods of calculating the effective or equivalent over-alllever arm or torque factor for a pumping unit at any given position ofits stroke from the basic geometrical relationships of the unit layoutare by now well known, having been worked out under the auspices of theA.P.I. and adopted throughout the industry. (See, for example, thebrochure by D. 0. Johnson entitled Torque Factors for Pumping Units,published as part of the Proceedings of the West Texas Oil Lifting ShortCourse of April 1959.) Thus, it is known that these torque factors canbe calculated from the following equation:

AR sin a T. Factor T X sin 5 where A is the length of the well workingarm of the walking beam, i.e., the horizontal distance between thesaddle bearing pivot point and the center line of the well,

R is the crank arm length, i.e., the radius of the circle of rotation ofthe wrist pin,

C is the distance between saddle bearing and tail bearing pivot points,

a is the angle between the pitman arm and the crank arm,

and

B is the angle between the pitman arm and the straight line connectingtail bearing and saddle bearing pivot points.

Since A, R and C all remain constant throughout the full stroke cycle ofa unit, the variations which occur in torque factor values during thestroke will obviously be determined by the interrelationships betweenangles a and ,8.

Using the above relationship, the torque factors were calculated atfrequent intervals throughout the pumping stroke cycles of each of theunit layouts represented by the cases set forth in Table I above, thelength of the well working arm, A, employed in each set of calculationshaving been first selected so that each layout would deliver the sameactual well working stroke, namely 74 inches. In this way the maximumtorque factor during the upstroke and the maximum torque factor duringthe downstroke were determinedfor each of the four cases specified inTable I with the following results:

TABLE II [all values in inches] Case Max. T. factor Max. T. factor Sumof Max.

(upstroke)" (downstroke) '1. factors Figure 2 32. 43 39. 93 72. 36Figure 3 (iorward). 35. 07 38. 58 73. Figure 3 (rear)..- 26. 32 42. 1O68. 42 Figure 4 32. 38 39. 73 72. 11

*For clockwise rotation of the cranks.

3, i.e., with the crankshaft located at point C as a practical matterthis location is less desirable than the others illustrated because, asa result of the magnitude of the forces involved, excessively large andheavy hearing assemblies would be required. Furthermore, said cranklocation, C as depicted in the rear layout of FIGURE 3, is in closeproximity to the limit line (dotted line LX) at which the pitman couldbreak downward at the tail bearing connection when it reaches point L(i.e., at the top of the unit stroke).

The forward layout of FIGURE 3 with the crank shaft at point Crepresents a preferred limiting position in the other direction for aunit layout in which the crank and pitman arm lengths are exactly thesame as in the setup depicted in FIGURE 2 and in the rear layout ofFIGURE 3. Thus, as suggested by the relatively small reduction in sum ofmaximum torque factors shown in Table II above for the case of FIGURE 3(forward), further movement of the crank shaft toward the well along thearc C -C will cause a general increase in torque factors so that the sumof the two maxima therein will exceed the stroke. Therefore, location ofthe crank shaft in accordance with the present invention should besufficiently to the rear of the tail bearing so that substantially theentire circle of rotation of the wrist pin lines to the rear of thestraight line through the tail hearing at its lowest point L and runningat right angles to the line (MS) between the saddle bearing and the tailbearing at its midstroke position.

For best results the crank will be located in the middle ground betweensaid extreme positions such as at point C of FIGURE 3 (which representsthe location laid out in detail in FIGURE 2), or such as that shown inFIG- URE 4 for a unit with a different pitman arm to crank arm ratio. Inshort, it can be seen from the above considerations balancing over-allefiiciency with utility, soundness and economy of construction, and easeof maintenance, the crankshaft should be located so that substantiallythe entire circle of rotation of the wrist pin lies with an elevationalarea such as that in the lower left hand corner of FIGURE 4 (below lineXL and to the left of line LZ).

In addition to the improved over-all efiiciency indicated by theover-all reduction in torque factors attained, several other definiteadvantages accrue from the present invention. Thus, as is indicated bythe figures on maximum torque factors given in Table II above, thetorque factors on the upstroke for clockwise rotation of the crank inunits of this invention are substantially lower over practically thefull cycle than the respective figures at corresponding positions of thedownstroke. This is most beneficial since it tends to provide inherentcompensation for the increased well load at the polished rod due to thedifferential weight of fluid lifted and delivered each stroke.Consequently, the actual well load torques applied to the crank duringthe downstroke tend to approach those on the upstroke much more closelythan in previous designs of conventional units, thus greatly decreasingones dependence upon the use of crank weight counterbalancing and,accordingly, the amount of counterweights which must be provided andused in practice.

It will also be seen from the diagrams of FIGURES 2 through 4 that theangle b representing the position of the crank in a clockwise directionbeyond its 12 oclock or 0 position at the end of the upstroke is alwaysmore than 180 greater than angle a, representing the position of crankat the beginning of the upstroke. The accurate figures for the fourcases illustrated in FIGURES 2 through 4 are given in the followingtable.

Thus, it will be seen that, for clockwise rotation of the crank asviewed in the drawings, the period of the crank rotation cycle devotedto the upstroke is always somewhat greater than If the speed of rotationof the crank is at all constant, this means that the present unit willfavor movement of the rod string on the downstroke at an averagevelocity higher than that on the upstroke, thus providing a situationmuch more in harmony with the way other factors and natural phenomena,such as gravity, tend to influence the motion of the rod string. Thus,the decreased instantaneous speeds on the upstroke help to avoid addingextra dynamic load due to frictional effects, etc., at the very timewhen the inertial loading itself is already high. Furthermore, moderateincreases in down hole instantaneous speeds are generally in line withthe natural acceleration of the rod string due to gravitational pull.However, the downstroke acceleration must not be increased to the pointof causing separation of the polished rod clamp and wire line hanger tooccur since this might damage the polished rod or other parts of thepumping unit. For this reason, it is not recommended that the upstrokeperiod of the pumping cycle occupy substantially more than about 210 outof the 360 total.

Considering all the above factors, it can be stated as a general rule,therefore, that the location of the crank shaft should be to the rear ofthe specified straight line through the tail bearing (such as LZ) by adistance at least as great as about one quarter the length of the pitmanarm but not greater than about two thirds of said pitman arm length sothat the angle a at the beginning of the upstroke will be at least about7 and not substantially greater than about 35 and the difference betweenangle b and angle a will not be substantially less than about norsubstantially more than about 210.

As already mentioned in connection with the description of the unitshown in FIGURE 1, the most common method of providing counterbalance inpumping units of the walking beam type is the addition of weights eitheron the crank arm or on the walking beam itself. It is, of course,obvious that the moment exerted by a given mass of such counterweightswill increase as the center of mass of said weights is moved out fromthe crank shaft or the saddle bearing respectively, but there arenaturally practical limits on such distances. Thus, any decrease in needfor and dependence on counterweights is always a definite advantage.However, it is of even greater advantage in the present inventionbecause, the counter-moment produced by a crank-attached counterweightbeing inherently a perfectly regular sinusoidal function, specialproblems are presented in the use of crank-attached counterweights tocounterbalance a unit like the present ones in which the deviation ofthe actual dynamic well load on the crank from a regular sine wave isfurther exaggerated due to the appreciable differential between upstrokeand downstroke periods. Accordingly, in many units designed inaccordance with the present. invention, the reliance on crankattachedcounterweights can be sufficiently minimized that counterweights can bemounted on the crank shaft in the same manner most commonly used forconventional units, that is in line radially with the crank arm as shownin FIGURE 1.

Naturally, if the effect of the crank-attached counterweights assumessufiicient importance, they can also be mounted in such a way as to actsomewhat out of phase with the drive crank itself. For example, this canbe accomplished by using adjustable, or spreadable multipiece (e.g.,sheave or butterfly) type counterweights, which permit angularadjustment in the center of mass of such weights with respect to thecrank mounting even when mounted directly on the crank arm as shown inFIG- URE 1. Alternatively, as shown in FIGURE 5, a separatecounterweight arm 19 can be provided which is angularly offset withrespect to crank arm 23 b an angle d for example. Also, here again, thecrank weights 32 can be adjustable, e.g., from position 32 to position32, so

dotted lines of FIGURE 5. As a compromise arrangement.

for those intermediate cases where the crank-attached. counterweightsrepresent a factor too important to per; mit the use of an ordinaryfixed mounting radially in line with the crank arm itself but notsufliciently important to justify an angularly adjustable mounting, itis recommended that the counterweight mounting arm be offset so that thecrank weights exert their maximum effect (i.e., so that their center ofgravity reaches the 90 and 270. positions of rotation about thecrankshaft) .when the pumping unit is at approximately its midstrokeposition.-

In order to demonstrate apreferred embodiment of the present inventionand the valuable advantages obtainable through actual operation thereof,the following detailed specific example is presented.

EXAMPLE 1 A complete pumping unit was assembled with a drivesystemconforming closely in layout with that shown in FIGURE 2. Thus, theheight of the saddle bearing pivot point S on top of the samson post 12was about 17 feet above the bottom of the base, while the pitman armsand crank arms were 118.4 and 29.6 long respectively (P/R=4.0). With adistance of 96.2 between saddle bearing and tail bearing pivot points,the mulehead was located on the walking beam so as to give a pumpingstroke length of 74 inches, which required a well working arm of about105.7 inches (i.e., the horizontal distance from saddle bearing pivotpoint to vertical centerline of the well). The maximum torque factorsand the angular positions of the wrist pins at the beginning and end ofthe upstroke are accordingly as set forth in Tables II and Inhereinabove for the FIGURE 2 case.

Since it was found that the wrist pins reached a clockwise position ofabout 110 at the midpoint in the up.- stroke of this unit, acounterweight arm was mounted on the crank shaft having a centerline 20behind the radial line between the wrist pins and the center of thecrank shaft so that the center of gravity of the crank mountedcounterweights would reach the 90? or 3 oclock position of maximumtorsional effect exactly at this midstroke position.

This unit was tested by using it to lift oil from an actual well havinga fluid level about 2750 feet below ground.

Its performance on this well was compared directly.

against a conventional pumping unit of the same structural capacity andstroke length of 74". Both units were tested at pumping speeds of 10,and strokes per minute using the same electric prime mover (a H.P.440volt GE motor) for both in order to avoid motor speed torque variations.Since the conventional unit had a substantially symmetrical crank shaftlocation, i.e., substantially directly under the tail bearing, thecounterweights for this unit were mounted radially in line with thecenter of the crank shaft and the wrist pins, rather than out of phasetherewith.

During these comparison tests described above, a reduction in peaktorque at the crank of between about 21 and 34% (depending mostly onpumping speed) was ex: perienced onv the unit of the present inventionover that on the conventional unit, with an average reduction of about28%. Likewise a significant reduction in crank counterweights (averagingabout 13.5%) was successfully effected with the experimental unit.Likewise, the average power demand was reduced by about 17% with the newunit over that of the conventional apparatusiThis,

indicates that significant reductions in size and capacity of both primemovers and speed reducers would, be possible through use of theapparatus of this invention. 7

Investigations with other pumping units constructed in accordance withthe present invention and having,ditferent pitman arm toicrank armratios, such as 5 to 1 or 3 to 1 indicate that similar advantages can beobtained over the entirepracticalrange of P/R .ratios extending betweenabout 2.5 and 6.0. i I Having thus described our invention in detailtogether with preferred, illustrative embodiments thereoflwhatwe claimand desire to secure by US. Letters Patent is: k p

.1. In an oil well pumping device of the type in which reciprocation ofthe sucker'rod string in thewell casing is effected by attaching saidrod string to onearm of an oscillatory walking beam pivotally mounted bya saddle bearing near the medial portion thereof to a samson post,

. said walking beam having, on the'other arm thereof a tail bearingpivotally connected to a pitman arm the oppos'ite end of which isequipped with a Wrist pin attached piv? otally to a rotary crank -ttie'length of which is riotless than /6' the length of said pitman'arm,said crankbeing mounted on a shaft which bears counterbalancing weightsthereon and is positively driven in a clockwise direction as viewed withthe well working end of theunit to the right, 'the improvement whichcomprises locating said crank shaft out from under the area directlybeneath the operating arc of said tail bearing andso that substantiallythe entire circle of rotation of said wrist 'pin'lies to the.

rear of a straight line passing through the center of said tail bearingand drawn at right angles to the straight line connecting said tailbearing and said saddle hearing at the midstroke position of the unit.

2.' The improvement in an oil Well pumping device as specified in claim1 in which the position of said counterbalancing weights on said shaftis such that the center of gravity of said weights lags behind the wristpin position asthe crank rotates in said clockwise direction.

3. The improvement in an oil well pumping device as specified in claim 2in which the position of the center of gravity of said counterweights isset so that said center of gravity will be at the 3 oclock or positionof its rotation clockwise about the crank shaft when the well workingend of the walking beam has moved to the midpoint of its upstroke.

4. In oil well pumping devices of the type in which reciprocation of thesucker rod string is effected by attaching said string to one arm of anoscillatory walking beam mounted near the medial portion thereof bymeans of a pivotal connection atop a samson post, said beam being drivenby a pitman pivotally depending from a tail hearing on the other arm ofsaid beam which pitman is pivotally connected in turn to a rotary crankmounted on a driven shaft having counterbalancing weights mountedthereon, the improvement which comprises proportioning and arranging thelocation of the several elements so that the effective pitman to crankratio is between 2.5/1 and 6/1 and the crank shaft is suflicientlyspaced from the samson post so that it is out from under the areabeneath the operating arc of said tail bearing and so that substantiallythe entire circle of rotation of the pivot point of the connectionbetween crank and pitman lies to the opposite side' from the well andsamson post of a straight line passing through the tail bearing pivotpoint at its lowest point of travel and drawn at a right angle to thestraight line between the saddle bearing pivot point and the tailbearing pivot point at its midstroke position thereby producing acombination of torque factors such that the sum of the peak upstroke andpeak downstroke torque factors is less than the actual stroke lengthdelivered by the pumping device so assembled.

5. The improvement in oil well pumping devices as specified in claim 4in which the said counterbalancing weights are mounted from said crankshaft in a position sufiiciently offset in a counterclockwise directionfrom the radial position of the crank that the center of gravity of saidWeights will be at the 3 oclock or 90 position of clockwise rotationabout the crank shaft just as the Walking beam reaches the midpoint ofthe upstroke on the rod string, thereby providing maximum torsionaleffect of said counterbalancing Weights on said crank shaft at about thesame time as the peak upstroke torque factor occurs.

6. The improvement in oil well pumping devices as specified in claim 4in which the location of the drive shaft is also such as to place thecenter of said shaft not more than about two thirds of the effectivepitman length behind the straight line drawn through the tail bearingpivot point at its lowest position and at right angles to the straightline connecting the saddle bearing pivot point of the beam on top of thesamson post with the tail bearing pivot point at the midstroke positionof the unit.

References Cited UNITED STATES PATENTS 1,890,807 12/1932 Faber 74411,917,701 7/1933 Crites et al. 74-41 3,310,988 3/1967 Gault 74-41 MILTONKAUFMAN, Primary Examiner.

